1. Field of the Invention
The present invention relates to equipment for levelling and densifying plastic concrete, and more particularly, to equipment which both levels and internally vibrates plastic concrete.
2. Description of the Prior Art
Before applicant's invention of the apparatus disclosed herein, a person of ordinary skill in the art suggested the desirability of pouring plastic concrete in a thickness greater than ultimately required, internally vibrating that mass of concrete and subsequently removing the excess or surcharge layer of concrete to achieve a stronger and more durable concrete deck. Structure for accomplishing that objective was not disclosed.
The prior art discloses a wide variety of mechanical internal vibration devices for compacting and densifying plastic concrete. U.S. Pat. No. 4,128,359 (Cooper) discloses a self-propelled concrete vibrator apparatus which includes a plurality of hydraulically powered vibrators positioned at evenly spaced apart intervals across the full width of a support truss. This device includes a plurality of hydraulic rams which raise and lower the plurality of vibrator units into and out of a mass of wet concrete. A second group of horizontally oriented hydraulic rams is coupled to the plurality of vibrator units and laterally displaces the vibrator units between a first and a second position. This device includes an hydraulic pump driven by an internal combustion engine and a plurality of four drive units for longitudinally translating the entire structure along the length of the concrete to be vibrated.
U.S. Pat. No. 2,223,734 (Mall) discloses a concrete vibrator which is longitudinally translatable along the length of an area of wet concrete. This device includes a vibrator carriage to which an engine is mounted. This vibrating carriage is longitudinally translatable between a first and a second position and includes a centrally mounted shaft which permits the carriage to be pivoted and to thereby partially elevate the mechanically driven concrete vibrators with respect to the surface of the wet concrete. U.S. Pat. No. 2,248,103 (Mall) discloses an attachment for a screed which includes a laterally oriented frame having a plurality of evenly spaced apart vibrators. A hand actuated lever permits an operator to simultaneously raise or lower all of the vibrators with respect to the surface of the wet concrete. U.S. Pat. No. 1,945,145 (Gordon) discloses an apparatus for compacting and dewatering wet cement. The body of this device includes a hand operated lever which permits the entire device, including a plurality of vertically oriented fixed position vibrators and the vacuum chamber of the invention, to be raised or lowered with respect to the surface of the concrete. In the raised position, the entire device can be longitudinally translated with respect to the wet concrete.
U.S. Pat. No. 2,138,103 (Jorgensen) discloses a road paving machine which includes four motor driven vibrators which are mounted in laterally fixed positions to a longitudinally translatable carriage. A strike off bar is coupled to the carriage at a position behind the vibrator unit. A hand wheel in combination with a worm gear permits the vibrator assembly to be raised or lowered with respect to the surface of the concrete. When the vibrators are lowered into the surface of the concrete and the machine is advanced, the vibrators are deflected to the rear and are dragged through the surface of the wet concrete.
U.S. Pat. No. 2,382,096 (Pierce) discloses a paving machine having a plurality of vibrator units mounted at fixed positions laterally across the face of the device. The vibrators span the entire width of the wet concrete surface to be vibrated. This device includes a concrete screed and is hydraulically powered. The plurality of vibrators are pivoted about a point and inserted at an angle into the wet concrete in a manner which permits the vibrators to travel beneath the concrete screed.
U.S. Pat. No. 2,292,733 (Baily) discloses a concrete vibrating device including a plurality of vibrators mounted at a fixed position along the entire width of the device. The vibrators are flexibly coupled to the frame which permits them to be deflected to the rear of the frame as it advances through the concrete. U.S. Pat. No. 2,461,500 (Miller) discloses an apparatus for compating concrete slabs which includes a plurality of vibrator units mounted at fixed positions laterally across the device. Each vibrator is driven by a motor coupled to a flexible shaft. The vibrators trail behind and penetrate below the surface of the wet concrete as the device is advanced through the concrete.
U.S. Pat. No. 3,555,983 (Swisher) discloses a paving grout control device which includes vibrator units positioned at evenly spaced intervals laterally across the front of the device. This device includes a comb-like structure which is immersed at a point behind the vibrating units at a predetermined depth into the paving material. U.S. Pat. No. 2,148,214 (Mall) discloses a vibrating machine which includes an inverted "T"-shaped horizontally oriented vibrating tube which is immersed into the wet concrete. U.S. Pat. No. 2,233,833 (Jackson) discloses a related device having three horizontally oriented vibrating tubes which vibrate the wet concrete. A screed also forms a part of this device which serves to level the surface of the wet concrete. U.S. Pat. No. 3,113,494 (Barnes) discloses a machine for finishing concrete surfaces and includes a mechanically vibrated screed. This device is laterally translated by a pair of manually operated winches one of which is coupled to each end of the frame of this device.
The following U.S. patents disclose inventions relevant to applicant's invention: U.S. Pat. No. 1,747,555 (Pelton); U.S. Pat. No. 2,030,315 (Noble); U.S. Pat. No. 1,898,158 (Winkler); and U.S. Pat. No. 3,413,902 (Malan).
Many of the devices discussed above are hydraulically powered and include hydraulically driven vibrator devices. Hydraulically powered vibrating equipment is comparatively heavy since the hydraulic power source is typically mounted to the frame of the vibrating device. The weight of this hydraulically powered vibrating equipment is further increased since the frame itself must be heavier to support the substantial weight of the hydraulic power source.
Virtually all of the devices described above incorporate a plurality of vibrator units which are mounted at uniformly spaced apart intervals across the full span of the supporting frame. If any particular prior art concrete vibrating device can be modified to vibrate different widths of concrete surfaces, the width of the supporting frame must be modified and a corresponding number of vibrating units must either be added to or subtracted from the device. This particular requirement not only increases the weight of the equipment which has been adapted to vibrate wide concrete surfaces, but also substantially increases the cost of a widened device since each vibrator unit is a highly specialized, high cost piece of equipment. The addition of vibrator units to a widened device also requires that the hydraulic or mechanical power unit produce an increased amount of power to drive the added vibrator units.